Induction of perlecan gene expression precedes amyloid formation during experimental murine AA amyloidogenesis

BACKGROUND: In a murine model of AA amyloidosis, it has been demonstrated that perlecan, the basement membrane heparan sulfate proteoglycan, is co-deposited with AA amyloid as it forms in various tissues. The objectives of this study were to determine whether the accumulation of perlecan during amyloidogenesis is associated with induction of perlecan gene expression and, if so, to define the temporal relationship of this induction to the onset of amyloid formation. EXPERIMENTAL DESIGN: Accelerated splenic AA amyloidosis was stimulated in mice by concomitant administration of subcutaneous silver nitrate as an inflammatory stimulus and amyloid-enhancing factor. A kinetic analysis of splenic perlecan mRNA levels during amyloid formation in the spleen was conducted using a reverse transcription-polymerase chain reaction assay. Amyloid deposits were detected histochemically with the Congo red stain and by immunohistochemistry using anti-AA antisera. RESULTS: Perlecan mRNA levels increased significantly during amyloidogenesis, increasing 4.1-fold within 72 hours of the amyloidogenic stimulus and subsequently falling to steady-state levels. A 2.0-fold induction of perlecan mRNA occurred by 24 hours post-stimulation, a time at which amyloid was not detectable by either histochemistry or immunohistochemistry. In contrast, control animals administered either the inflammatory stimulus or AEF alone showed no significant change in perlecan mRNA levels. CONCLUSIONS: Increased perlecan mRNA levels account, at least in part, for the accumulation of perlecan in murine splenic AA amyloid deposits. This induction of perlecan gene expression occurs before the onset of amyloid formation, supporting a role for perlecan in the earliest stages of amyloid fibrillogenesis.